Hydraulic brake fluid



United States Patent HYDRAULIC BRAKE FLUID George L. Doelling and Chester B. Swander, St. Louis, Mo., assignors to Wagner Electric Corporation, St. Louis County, Mo., a corporation of Delaware No Drawing. Continuation of abandoned application Serial No. 303,617, August 9, 1952. This application April 25, 1956, Serial No. 580,455

14 Claims. (Cl. 252-79) This invention relates to fluids for use in pressure systems. More particularly it relates to hydraulic brake fluids, especially to brake fluids usable at extremely low temperatures as well as at temperatures usually encountered in the operation of automobiles, buses, trucks or military vehicles.

This application is a continuation of our copending application Serial No. 303,617, filed August 9, 1952, entitled Brake Fluid, now abandoned.

The principal object of the present invention is to provide suitable fluids for actuating hydraulic brakes and other pressure systems on automobiles, trucks, buses, military vehicles and wherever hydraulic brakes are used, ineluding so-called industrial brakes such as crane brakes, etc.

Another object of this invention is to provide hydraulic brake fluids which will operate satisfactorily even under severe conditions of operation. Many of the brake fluids used in passenger cars in the past are not suitable or safe for heavy-duty use in trucks, buses and military vehicles or under severe conditions of temperature or climate. 7

The new brake fluids of this invention are characterized by the property of being operative at extremely low winter temperatures, such as is required in military vehicles in nothern climates, as well as in summer weather in milder-climates, and under heavy-duty conditions.

This invention comprises hydraulic brake fluids having ingredients and combinations of ingredients, the proportions thereof, and features of composition and synthesis, which will be hereinafter described and claimed.

The generally accepted requirements of a satisfactory hydraulic brake fluid are as follows:

It must be sufiiciently high in boiling point so that it does not vaporize while in use in the system. It must notfreeze or solidify even at extremely low winter temperatures. Its viscosity at low temperatures must not be over about 2200 centistokes at the lowest temperature encountered in use. It must not corrode metals or have a swelling or deleterious effect on rubber sealing elements. Also, good lubricating value, water-tolerance, stability under heat, and miscibility with other brake fluids, are required.

.One difliculty with brake fluids to date has been that if a suflicient amount of lubricant, such as castor oil or ricinoleate ester, was used to give good lubricating value, then the fluid would have inferior low-temperature properties, a high viscosity or actually would freeze up at low winter temperatures. Since certain specifications for brake fluids now require at least 20% by weight of nonvolatile lubricant element, such as castor oil, it is diflicult to meet this requirement and also meet the ever-increasing requirement for low freezing point and low viscosity at low temperatures.

To meet these requirements, and also the requirement that the lubricant element of the brake fluid should not be soluble in water, we have found that if as the lubricant element of a brake fluid, part of the lubricant is a glycol ricinoleate and part of it is an insoluble polypropylene glycol, then all of these requirements are met.

The brake fluid of this invention contains as the waterinsoluble lubricant element a mixture of a n'cinoleate of an aliphatic glycol and a water-insoluble polypropylene glycol, having an average molecular weight of 1,000 to 3,000. As the diluent element this fluid contains a diluent selected from the group consisting of methoxybutanol and the lower (C -C mono-alkyl ethers of diethylene glycol. In addition, a relatively smaller amount of one or more glycols such as propylene, butylene or hexylene glycol, and a corrosion inhibitor and an antioxidant may be used.

Our preferred composition comprises from 5 to 20% by volume of a ricinoleate of a glycol, said glycol being an aliphatic glycol having not over five carbon atoms per molecule, from 5% to 20% by volume of a waterinsoluble polypropylene glycol having an average molecular weight from 1,000 to 3,000, from 50% to by volume of at least one diluent chosen from the group consisting of methoxy-butanol and the lower (C -C mono-alkyl ethers of diethylene glycol, from 5% to 25 v This composition makes it possible to meet the stringent requirements of a so-called heavy duty brake fluid and.

still have in it a considerable amount of the castor-base type of lubricant which gives good lubricating and corrosion-resisting properties .to the fluid. This has not been previously accomplished because the castor-base lubricants, where used alone, do not give a fluid which will meet the rigid freezing point and low-temperature water-tolerance tests specified for such heavy duty brake fluids. This novel composition also makes it possible to produce brake fluids in quantity even when the supply of castor oil is limited, as is often the case, especially in time of war. In the lubricant element of the fluid, the ricinoleates of the lower aliphatic glycols and di-glycols are preferred since they are stable, give good lubricating qualities to the fluid, and do not cause the fluid to congeal or freeze up at low temperatures as readily as does castor oil for example. Propylene glycol mono-ricinoleate is the preferred ricinoleate ester in this composition. Di-ethylene glycol ricinoleate and butylene glycol ricinoleate can also be used. A substantially water-insoluble polypropylene glycol having an average molecular weight of from 1,000 to 3,000 is also used in the lubricant element of swells rubber to some extent, and has less lubricating value than the 1000 to 3000 molecular weight product.

The diluent or viscosity-reducing agent in our preferred fluid may be a glycol-ether such as B-methoxybtitanol or diethylene glycol mono-ethyl ether or other lower monoalkyl ether of diethylene glycol. diethylene glycol mono-ethyl ether, the pure, so-called low-gravity grade should be used. The diethylene glycol mono-ethyl ether of the pure so-called low gravity grade has an ethylene glycol content of not more than approximately 3 percent ethylene glycol by volume. Since the commercial product may contain as much as 20% or more of ethylene glycol, it is not suitable for use in-this 1 or high-gravity:

composition. The regular commercial grade of diethylene glycol mono-ethyl ether is not suit- When the diluent is able for this use because it is more corrosive, but chiefly because the viscosity of the brake fluid made with it becomes so high at 40 F. and 60 F., that it is either marginal or outside of the usual specification limits. Fluids made with the same ratio of ingredients, but using the pure low-gravity grade, have viscosities that are easily within specification limits, as is shown by the examples.

To prevent attack on the metal parts of the brake sys tem a corrosion inhibitor may be used. Potassium ricinoleate, borax, sodium nitrite or diamylamine phosphate may be used, as well as an antioxidant such as diphenylol propane or hydroquinone or 2,6-di-tertiary-butyl 4-methy1 phenol. Usually about 0.2 to 3.0% of the corrosion inhibitor and from 0.1 to 0.5% of the antioxidant, on the weight of the fluid is suflicient for the purpose.

The heavy-duty brake fluid of this invention is surprisingly low in its eflect on rubber, especially when consideringthe very long temperature range this fluid has (from 60 F. to over 300 F.). Very high boilingpoint fluids are usually rather severe in their effect on rubber. In the stroking-tests and rubber-swelling tests described in the examples, the effect on rubber was unusually mild.

The proportions of the ingredients used in applicants composition are critical, and the proportions claimed are chosen because all of the numerous requirements of a commercially practicable brake fluid will not be satisfactorily met unless these proportions are used.

More specifically, the following examples will serve to illustrate the invention. These examples, which are illustrative of the various ratios orproportions, produce approximately 100 cc. of fluid.

7 Example No. 1

Diethylene glycol mono-ethyl ether (pure grade) cc 6.5 Polypropylene glycol (mol. wt. 2,000) cc 11.5 2-methyl-2,4-pentaneidiol cc 5.0 Propylene glycol cc .0 Propylene glycol mono-ricinoleate cc 12.5 Diphenylol propane grams 0.3 Potassium ricinoleate do 0.7

The 2-methy1-2,4-pentanediol is sometimes called hexylene glycol.

The brake fluid made up of the above ingredients had the following properties:

The corrosion test specified in the SAE hydraulic brake fiuidspecification was run on this fluid (5 days at 210 F.). The aluminum strip showed no loss in weight, the tinned iron, steel, cast iron and copper each lost about .02 milligram per square centimeter, and the brass strip lost .06 milligram per square centimeter. All of these results are far below the allowable loss given in the specification, which is 0.5 each for brass and copper,

-0.7 for tin, steel and cast-iron and 0.2 for aluminum.

The pH after the corrosion test was 7.6.

A stroking test according to the SAE specification was run on this fluid, and the results were satisfactory, indicating adequate lubricating properties in the fluid. Results after use of this brake fluid in test-cars also were satisfactory, showing that it is an operable hydraulic brake fluid;

4 Example N0. 2

Diethylene glycol mono-ethyl ether (pure grade) cc 70.0 Polypropylene glycol (mol. wt. 2,000) cc 11.5 Propylene glycol cc 5.0 Propylene glycol mono-ricinoleate cc 12.5 Diphenylol propane grams 0.3 Potassium ricinoleate do 0.7

The brake fluid made by mixing these ingredients had the following properties:

Specific gravity at 20 C. .993 Acid number 0.17 Viscosity at -40 F. centistokes 680 Viscosity at 68 F do 13 Boiling point, SAE F 381 Cold test, 6 hours at 6() F. Fluid The SAE corrosion test, 5 days at 210 F., on this fluid gave very satisfactory results. In every case, on tin, steel, aluminum, cast-iron, brass and copper, the loss in weight was less than 0.1 milligram per square centimeter, or far lower than the specification limit.

The rubber-swelling after 5 days at 70 C. on a 1% inch Manhattan cup was 4.95% by volume.

I Example N0. 3 Diethylene glycol mono-ethyl ether (pure grade) cc 60.0 Polypropylene glycol (mol. wt. 2,000) cc 7.5 Propylene glycol cc 4.2 2-methyl-2,4-pentanediol cc 10.0 Propylene glycol mono-ricinoleate cc 17.0 Diphenylol propane grams 0.3 Potassium ricinoleate do 1.0

The brake fluid made by mixing these ingredients had the following properties:

Specific gravity at 20 C. .984 Acid number 0.16 Viscosity at 68 F. centistokes 14.8 Rubber-swelling, 5 days at 70 0., gain in percent by volume 4.7 Boiling point F 379 Cold test, 6 hours at 60 F Fluid The regular SAE corrosion test, 5 days at 210 F., on this fluid gave losses in milligrams per square centimeter as follows:

The brake fluid made by mixing these ingredients had the following properties:

Specific gravity at 20 C Q. .951 Boiling point F 320 Viscosity at 68 F centistokes.. 19 Cold test, 6 hours at -60 F Fluid Rubber swelling, 5 days at 70 (3., gain in percent by volume What we claim is:

l. A heavy-duty hydraulic brake fluid consisting essentially of, per 100 parts by volume, 50 to 75 parts by volume of at least one diluent chosen from the group consisting of methoxy-butanol and the lower mono-alkyl ethers of diethylene glycol, said ethers being of a pure low gravity grade having an ethylene glycol content of not more than approximately 3 percent ethylene glycol by volume, from 5 to 20 parts by volume of a ricinoleate of a glycol, said glycol being an aliphatic glycol having not over five carbon atoms per molecule, from 5 to 20 parts by volume of a substantially Water-insoluble polypropylene glycol having an average molecular weight between 1,000 and 3,000, from 5 to 25 parts by volume of at least one glycol chosen from the group consisting of propylene glycol, butylene glycol and hexylene glycol, said polypropylene glycol plus said ricinoleate of a gycol forming a total of at least approximately 20 percent by weight of the brake fluid.

2. The fluid set forth in claim 1, wherein said fluid is provided with small but eflective amounts of antioxidant and corrosion inhibitor.

3. A heavy-duty hydraulic brake fluid consisting es: sentially of, per 100 parts by volume, 50 to 75 parts by volume of a diluent chosen from the group consisting of methoxy-butanol and the lower monoalkyl ethers of diethylene glycol, said ethers being of a pure low gravity grade having an ethylene glycol content of not more than approximately 3 percent ethylene glycol by volume, from 5 to 20 parts by volume of propylene glycol mono-ricinoleate, from 5 to 20 parts by volume of a substantially water-insoluble polypropylene glycol having an average molecular weight between 1,000 and 3,000, from 5 to 25 parts by volume of at least one glycol chosen from the group consisting of propylene glycol, butylene glycol and hexylene glycol, together with small but effective amounts of anti-oxidant and corrosion inhibitor, said polypropylene glycol plus said propylene glycol monoricinoleate forming a total of at least approximately 20 percent by weight of the brake fluid.

4. A heavy-duty hydraulic brake fluid consisting essentially of, per 100 parts by volume, 50 to 75 parts by volume of a diluent chosen from the group consisting of methoxy-butanol and the lower mono-alkyl ethers of diethylene glycol, said ethers being of a pure low gravity grade having an ethylene glycol content of not more than approximately 3 percent ethylene glycol by volume, from 5 to 20 parts by volume of propylene glycol mono-ricinoleate, from 5 to 20 parts by volume of a substantially Water-insoluble polypropylene glycol having an average molecular weight between 1,000 and 3,000, from 5 to 25 parts by volume of propylene glycol, together with small but eifective amounts or" anti-oxidant and corrosion inhibitor, said polypropylene glycol plus said propylene glycol mono-n'cinoleate forming a total of at least 20 percent by weight of the brake fluid.

5. A heavy-duty hydraulic brake fluid consisting essentially of, per 100 parts by volume, 50 to 75 parts by volume of a diluent chosen from the group consisting of methoxy-butanol and the lower mono-alkyl ethers of diethylene glycol, said ethers being of a pure low gravity grade having an ethylene glycol content of not more than approximately 3 percent ethylene glycol by volume, from 5 to 20 parts by volume of propylene glycol mono-ricinoleate, from 5 to 20 parts by volume of a substantially Water-insoluble polypropylene glycol having an average molecular weight of approximately 2,000, from 5 to 25 parts by volume of at least one glycol chosen from the group consisting of propylene glycol, butylene glycol and hexylene glycol, together with small but effective amounts of anti-oxidant and corrosion inhibitor, said polypropyleneglycol plus said propylene glycol mono-ricinoleate forming a total of at least 20 percent by weight of the brake fluid.

6. A heavy-duty hydraulic brake fluid consisting cssentially of, per parts by volume, 50 to 75 parts by volume of methoxy-butanol, from 5 to 20 parts by volume of propylene glycol mono-ricinoleate, from 5 to 20 parts by volume of a substantially water-insoluble polypropylene glycol having an average molecular weight between 1,000 and 3,000, from 5 to 25 parts by volume of at least one glycol chosen from the group consisting of propylene glycol, butylene glycol and hexylene glycol, together with small but eflective amounts of anti-oxidant and corrosion inhibitor, said polypropylene glycol plus said propylene glycol mono-ricinoleate forming a total of at least 20 percent by weight of the brake fluid.

7. A heavy-duty hydraulic brake fluid consisting essentially of, per 100 parts by volume, 50 to 75 parts by volume of diethylene glycol mono-ethyl ether, said ether being of a pure low gravity grade having an ethylene glycol content of not more than approximately 3 percent ethylene glycol by volume, from 5 to 20 parts by volume of propylene glycol mono-ricinoleate, from 5 to 20 parts by volume of a substantially Water-insoluble polypropylene glycol having an average molecular weight between 1,000 and 3,000, said polypropylene glycol plus said ricinoleate of a glycol forming a total of at least approximately 20 percent by weight of the brake fluid, and from 5 to 25 parts by volume of at least one glycol chosen from the group consisting of propylene glycol, butylene glycol and hexylene glycol, together with small but effective amounts of anti-oxidant and corrosion inhibitor.

8. A heavy-duty hydraulic brake fluid consisting essentially of, per 100 parts by volume, 50 to 75 parts by volume of a lower mono-alkyl ether of diethylene glycol, said other being of a pure low gravity grade having an .ethylene glycol content of not more than approximately 3 percent'ethylene glycol by volume, from 5 to 20 parts by volume of propylene glycol mono-ricinoleate, from 5 to 20 parts by volume of a substantially water-insoluble polypropylene glycol having an average molecuar weight between 1,000 and 3,000, said polypropylene glycol plus said ricinoleate of a glycol forming a total of at least approximately 20 percent by weight of the brake fluid, and from 5 to 25 parts by volume of at least one glycol chosen from the group consisting of propylene glycol, butylene glycol and hexylene glycol, together with a small but effective amount of corrosion inhibitor.

9. A heavy-duty hydraulic brake fluid consisting essentially of, per 100 parts by volume, about 65 parts diethylene glycol mono-ethyl ether, said ether being of a pure low gravity grade having an ethylene glycol content of not more than approximately 3 percent ethylene glycol by volume, about 11.5 parts of a substantially waterinsoluble polypropylene glycol having an average molecular weight of approximately 2,000, about 5 parts 2- methyl-Z, 4-pentanediol, about 5 parts propylene glycol, about 12.5 parts propylene glycol mono-ricinoleate, and a small but effective amount of corrosion inhibitor, said polypropylene glycol plus said ricinoleate of a glycol forming a total of at least approximately 20 percent by weight of the brake fluid.

10. A heavy-duty hydraulic brake fluid consisting essentially of, per 100 parts by volume, about 70 parts diethylene glycol mono-ethyl ether, said ether being of a pure low gravity grade having an ethylene glycol content of not more than approximately 3 percent ethylene glycol by volume, about 11.5 parts of a substantially water-insoluble polypropylene glycol having an average molecular weight of approximately 2,000, about 5 parts propylene glycol, about 12.5 parts propylene glycol monoricinoleate, and a small but effective amount of a corrosion inhibitor, said polypropylene glycol plus said ricinoleate of a glycol forming a total of at least approximately 20 percent by weight of the brake fluid.

11. A heavy-duty hydraulic brake fluid consisting essentially of, per 100 parts by volume, 50 to 75 parts by volume of diethylene glycol mono-ethyl ether, said ether being of a pure low gravity grade having an ethylene glycol content of not more than approximately 3 percent ethylene glycol by volume, from 5 to 20 parts by volume of a ricinoleate of'a glycol, said glycol being an aliphatic glycol having not over five carbon atoms per molecule, from 5 to 20 parts by volume of a substantially waterinsoluble polypropylene glycol having an average molecular weight between 1,000 and 3,000, from 5 to 25 parts by volume of at least one glycol chosen from the group consisting of propylene glycol, butylene glycol and hexylene glycol, together with small but effective amounts of anti-oxidant and corrosion inhibitor, said polypropylene glycol plus said ricinoleate of a glycol forming a total of at least approximately 20 percent by Weight of the brake fluid.

12. A heavy-duty hydraulic brake fluid consisting essentially of, per 100 parts by volume, 50 to 75 parts by volume of a lowermono-alkyl ether of diethylene glycol, said ether being of a pure low gravity grade having an ethylene glycol content of not more than approximately 3 percent ethylene glycol by volume, from 5 to 20 parts by volume of a ricinoleate of a glycol, said glycol being an aliphatic glycol having not over five carbon atoms per molecule, from 5 to 20 parts by volume of a substantially water-insoluble polypropylene glycol having an average molecular" weight, between 1,000 and 3,000, from 5 to 25 parts by volume of at least one glycol chosen from the group consisting of propylene glycol, butylene glycol and hexylene glycol, together with ,small but effective amounts of anti-oxidant and corrosion inhibitor, said polypropylene glycol plus said ricinoleate of a glycol forming a total of at least approximately 20 percent by weight of the brake fluid. 13. A heavy-duty hydraulic brake fluid consisting essentially of, per 100 parts by volume, about parts diethylene glycol mono-ethyl ether, said ether being of a pure low gravity grade having an ethylene glycol content of not more than approximately 3 percent ethylene glycol by volume, about 11.5 parts of a substantially Waterinsoluble polypropylene glycol having an average molecular weight of approximately 2,000, about 5 parts 2- methyl-Z, 4-pentanediol, about 5 parts propylene glycol, about 12.5 parts propylene glycol mono-ricinoleate, and small but eifective amounts of anti-oxidant and corrosion inhibitor, said polypropylene glycol plus said ricinoleate of a glycol forming a total of at least approximately 20 percent by weight of the brake fluid.

14. A heavy-duty hydraulic brake fluid consisting essentially of, per 100 parts by volume, about parts diethylene glycol mono-ethyl ether, said ether being of a pure low-gravity grade having an ethylene glycol content of not more than approximately 3 percent ethylene glycol by volume, about 11.5 parts of a substantially Water-insoluble polypropylene glycol having an average molecular weight of approximately 2,000, about 5 parts propylene glycol, about 12.5 parts propylene glycol monoricinoleate, and small but efiective amounts of anti-oxidant and corrosion inhibitor, said polypropylene glycol plus said ricinoleate of a glycol forming a total of at least approximately 20 percent by weight of the brake fluid.

References Cited in the file of this patent UNITED STATES PATENTS 2,232,581 Woodhouse Feb. 18, 1941 2,507,401 Doelling May 9, 1950 2,665,312 Ohlman et a1. Jan. 5, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,92%5'2'6 George L Doelling a1 It is hereby certified that error appears in the -printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

n I. "cc 0,5 reed Colua'a'li 3 lime 37, Example No. l 01:

I for "-pentanmdwl" sighed sealed. this 28th day oi June 196;).

(SEAL) Attest:

AXLENE Attesting Officer ROBERT C. WATSON Commissioner of Patents 

1. A HEAVY-DUTY HYDRAULIC BRAKE FLUID CONSISTING ESSENTIALLY OF, PER 100 PARTS BY VOLUME, 50 TO 75 PARTS BY VOLUME OF AT LEAST ONE DILUENT CHOSEN FROM THE GROUP CONSISTING OF METHOXY-BUTANOL AND THE LOWER MONO-ALKYL ETHERS OF DIETHYLENE GLYCOL, SAID ETHERS BEING OF A PURE LOW GRAVITY GRADE HAVING AN ETHYLENE GLYCOL CONTENT OF NOT MORE THAN APPROXIMATELY 3 PERCENT ETHYLENE GLYCOL BY VOLUME, FROM 5 TO 20 PARTS BY VOLUME OF A RICINOLEATE OF GLYCOL, SAID GLYCOL BEING AN ALIPHATIC GLYCOL HAVING NOT OVER FIVE CARBON ATOMS PER MOLECULE, FORM 5 TO 20 PATTS BY VOLUME OF A SUBSTANTIALLY WATER-INSOLUBLE POLYPROPYLENE GLYCOL HAVING AN AVERAGE MOLECULAR WEIGHT BETWEEN 1,000 AND 3,000, FROM 5 TO 25 PARTS BY VOLUME OF AT LEAST ONE GLYCOL CHOSEN FROM THE GROUP CONSISTING OF PROPYLENE GLYCOL, BUTYLENE GLYCOL AND HEXYLENE GLYCOL, SAID POLYPROPYLENE GLYCOL PLUS SAID RICINOLEATE OF A GYCOL FORMING A TOTAL OF AT LEAST APPROXIMATELY 20 PERCENT BY WEIGHT OF THE BRAKE FLUID. 